This invention relates to exhaust systems for internal combustion engines and, more particularly, to an exhaust system which attenuates exhaust sounds while maintaining relatively low back pressure for enhanced engine performance.
Conventional exhaust systems for internal combustion engines include mufflers connected to exhaust pipes through which the exhaust gases from the engine are passed to deaden and muffle the sound. Due to the flow resistance for gases passing through mufflers, such systems usually create significant amounts of pressure within the exhaust system upstream of the muffler or other flow restricting device. That pressure, known as "back pressure," is transferred further upstream through the system to the engine exhaust manifolds and ultimately affects overall engine performance. Particularly, in engines for sports cars and similar vehicles, increased back pressure can significantly reduce overall engine performance. In recent years, exhaust system back pressure has been even further increased due to the use of catalytic converters now mandated by federal law to cleanse exhaust gases of harmful emissions prior to entering the atmosphere.
In the past, some high performance vehicles, such as the Chevrolet Corvette.TM. or other sports vehicles, have incorporated exhaust systems running from the engine manifold directly back to side mounted pipes wherein the exhaust outlet is routed to the side of the vehicle between the front and rear wheels. Such side pipes create a high performance appearance for the vehicle as well as a deeper, high performance exhaust sound. Typically, these side pipes have included an exhaust pipe mounted within a larger pipe with some type of packing material therebetween, at least in the section of the system extending along the side of the vehicle immediately ahead of the exhaust outlet. The innermost pipe in such system is usually constricted at spaced locations to help muffle and/or tune the exhaust sounds, thereby creating performance reducing back pressure. In addition to the problem of increased back pressure, the mandatory inclusion of catalytic converters for cleansing exhaust gases has made the use of such side outlet exhaust pipes difficult. Moreover, at the portions of the exhaust system exposed along the vehicle sides, the exhaust pipes could become dangerously hot and injure persons who were unaware of the system condition.
Coupled with the above problems, prior known exhaust systems, especially side pipe systems, were often difficult to install on existing vehicles, i.e., to convert such vehicles from stock, original equipment systems to higher performance systems. This was especially true on vehicles equipped with catalytic converters, the removal of which subjects the owner to possible legal sanctions. Moreover, once installed, such prior systems did not allow control over the exhaust sound emanating from the engine. If dissatisfied with the sound, the vehicle owner simply had to replace the entire system at considerable expense.
Accordingly, a need existed for an improved exhaust system for internal combustion engines especially of the higher performance variety, which system avoided substantial increases in back pressure which otherwise would detract from engine performance, allowed use with existing catalytic converter equipped vehicles, provided the ability to control engine exhaust sounds after installation of the system, avoided dangerously exposed, hot exhaust pipes, and provide for use in side pipe mounted systems, especially for high performance vehicles.